Pressurized inerting system

ABSTRACT

A system and method for providing dried inert gas to a protected space is disclosed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a division of U.S. application Ser. No. 16/149,736,filed Oct. 2, 2018, now U.S. Pat. No. 11,679,893 the disclosure of whichis incorporated by reference herein in its entirety.

BACKGROUND

The subject matter disclosed herein generally relates to systems forproviding inert gas, and more particularly to inerting systems foraircraft fuel tanks.

It is recognized that fuel vapors within fuel tanks become combustibleor explosive in the presence of oxygen. An inerting system decreases theprobability of combustion or explosion of flammable materials in a fueltank by maintaining a chemically non-reactive or inert gas, such asoxygen-depleted air, in the fuel tank vapor space, also known as ullage.

It is known in the art to equip aircraft with onboard inert gasgenerating systems, which supply oxygen-depleted air to the vapor space(i.e., ullage) within the fuel tank. The oxygen-depleted air has asubstantially reduced oxygen content that reduces or eliminatesoxidizing conditions within the fuel tank. Some onboard inert gasgenerating systems generate humid oxygen depleted air. Methods andapparatus to reduce the water content of the humid oxygen-depleted airare needed.

BRIEF DESCRIPTION

A system for providing inert gas to a protected space, comprising apressurized air flow path in operative fluid communication with a boostcompressor and a chemical inert gas generator; and an inert gas flowpath in operative fluid communication with the chemical inert gasgenerator, a condenser and the protected space, wherein the condenseroperates at a pressure greater than or equal to 2 atmospheres absolutepressure and is located between the chemical inert gas generator and theprotected space along the inert gas flow path.

In any one or combination of the foregoing embodiments, the chemicalinert gas generator may include a catalytic oxidation unit. Thecatalytic oxidation unit may operate at a temperature greater than 150°C.

In any one or combination of the foregoing embodiments, the chemicalinert gas generator may include a proton exchange membraneelectrochemical device. The pressurized air flow path may furtherinclude a heat exchanger. In any one or combination of the foregoingembodiments, the pressurized air flow path includes a heat exchangerbefore the boost compressor and an additional heat exchanger after theboost compressor.

In any one or combination of the foregoing embodiments, the chemicalinert gas generator may include a solid oxide electrochemical device.The solid oxide electrochemical device may operate at a temperaturegreater than 700° C. The inert gas flow path may further include a heatexchanger between the chemical inert gas generator and the compressor.

In any one or combination of the foregoing embodiments, the pressurizedair flow path includes a bypass valve in parallel with the boostcompressor.

Also disclosed is a method for providing inert gas to a protected spacecomprising providing air having a pressure greater than or equal to 2atmospheres absolute pressure to a chemical inert gas generator;producing an inert gas in the chemical inert gas generator; providingthe inert gas to a condenser at a pressure greater than or equal to 2atmospheres absolute pressure; reducing the water content of the inertgas in the condenser; and providing the dried inert gas to a protectedspace.

In any one or combination of the foregoing embodiments, the chemicalinert gas generator may include a catalytic oxidation unit. Thecatalytic oxidation unit may operate at a temperature greater than 150°C.

In any one or combination of the foregoing embodiments, the chemicalinert gas generator includes a proton exchange membrane electrochemicaldevice. The proton exchange membrane electrochemical device may operateat a temperature less than the boiling point of water.

In any one or combination of the foregoing embodiments, the chemicalinert gas generator comprises a solid oxide electrochemical device. Thechemical inert gas generator may operate at a temperature greater than700° C.

BRIEF DESCRIPTION OF THE DRAWINGS

The following descriptions should not be considered limiting in any way.With reference to the accompanying drawings in which like elements arenumbered alike:

FIG. 1A is a schematic illustration of an aircraft that can incorporatevarious embodiments of the present disclosure;

FIG. 1B is a schematic illustration of a bay section of the aircraft ofFIG. 1A;

FIG. 2 is a schematic illustration of a chemical inert gas generator foran oxygen depletion system; and

FIGS. 3-5 are schematic illustrations of chemical inert gas generationsystems.

DETAILED DESCRIPTION

A detailed description of one or more embodiments of the disclosedapparatus and method are presented herein by way of exemplification andnot limitation with reference to the Figures.

As shown in FIGS. 1A-1B, an aircraft includes an aircraft body 101,which can include one or more bays 103 beneath a center wing box. Thebay 103 can contain and/or support one or more components of theaircraft 101. For example, in some configurations, the aircraft caninclude environmental control systems and/or fuel inerting systemswithin the bay 103. As shown in FIG. 1B, the bay 103 includes bay doors105 that enable installation and access to one or more components (e.g.,environmental control systems, fuel inerting systems, etc.). Duringoperation of environmental control systems and/or fuel inerting systemsof the aircraft, air that is external to the aircraft can flow into oneor more ram air inlets 107. The outside air may then be directed tovarious system components (e.g., environmental conditioning system (ECS)heat exchangers) within the aircraft. Some air may be exhausted throughone or more ram air exhaust outlets 109.

Also shown in FIG. 1A, the aircraft includes one or more engines 111.The engines 111 are typically mounted on the wings 112 of the aircraftand are connected to fuel tanks (not shown) in the wings, but may belocated at other locations depending on the specific aircraftconfiguration. In some aircraft configurations, air can be bled from theengines' 111 compressor stages and supplied to environmental controlsystems and/or fuel inerting systems, as will be appreciated by those ofskill in the art.

The fuel inerting system treats the air provided to the system to formoxygen-depleted air (ODA). The ODA is provided to a protected space suchas a fuel tank. There are several known methods of producing ODA onboard an aircraft which can produce humid ODA. These involve chemicalreactions such as those in the catalytic oxidation of fuel as well as inthe electrochemical reduction of oxygen at the cathode of anelectrochemical cell that utilizes proton exchange or oxygen aniontransport through the electrolyte. Catalytic oxidation of fuel isdescribed in U.S. Patent Publication No. 2018/0127110.

Referring now to FIG. 2 , a chemical inert gas generator comprising anelectrochemical cell is schematically depicted. The chemical inert gasgenerator 10 comprises a separator 12 that includes an ion transfermedium. As shown in FIG. 2 , the separator 12 has a cathode 14 disposedon one side and an anode 16 disposed on the other side. Cathode 14 andanode 16 can be fabricated from catalytic materials suitable forperforming the needed electrochemical reaction (e.g., theoxygen-reduction reaction at the cathode and an oxidation reaction atthe anode). Exemplary catalytic materials include, but are not limitedto, nickel, platinum, palladium, rhodium, carbon, gold, tantalum,titanium, tungsten, ruthenium, iridium, osmium, zirconium, alloysthereof, and the like, as well as combinations of the foregoingmaterials. Some organic materials and metal oxides can also be used ascatalysts, as contrasted to electrochemical cells utilizing protonexchange membranes where the conditions preclude the use of metal oxidecatalysts. Examples of metal oxide catalysts include, but are notlimited to ruthenium oxides, iridium oxides or transition-metal oxides,generically depicted as M_(x)O_(y), where x and y are positive numberscapable of forming a stable catalytic metal oxide such as Co₃O₄. Cathode14 and anode 16, including catalyst 14′ and catalyst 16′, are positionedadjacent to, and preferably in contact with the separator 12 and can beporous metal layers deposited (e.g., by vapor deposition) onto theseparator 12, or can have structures comprising discrete catalyticparticles adsorbed onto a porous substrate that is attached to theseparator 12. Alternatively, the catalyst particles can be deposited onhigh surface area powder materials (e.g., graphite or porous carbons ormetal-oxide particles) and then these supported catalysts may bedeposited directly onto the separator 12 or onto a porous substrate thatis attached to the separator 12. Adhesion of the catalytic particlesonto a substrate may be by any method including, but not limited to,spraying, dipping, painting, imbibing, vapor depositing, combinations ofthe foregoing methods, and the like. Alternately, the catalyticparticles may be deposited directly onto opposing sides of the separator12. In either case, the cathode and anode layers 14 and 16 may alsoinclude a binder material, such as a polymer, especially one that alsoacts as an ionic conductor such as anion-conducting ionomers. In someembodiments, the cathode and anode layers 14 and 16 can be cast from an“ink,” which is a suspension of supported (or unsupported) catalyst,binder (e.g., ionomer), and a solvent that can be in a solution (e.g.,in water or a mixture of alcohol(s) and water) using printing processessuch as screen printing or ink jet printing.

The cathode 14 and anode 16 can be controllably electrically connectedby electrical circuit 18 to a controllable electric power system 20,which can include a power source (e.g., DC power rectified from AC powerproduced by a generator powered by a gas turbine engine used forpropulsion or by an auxiliary power unit) and optionally a power sink.In some embodiments, the electric power system 20 can optionally includea connection to an electric power sink (e.g., one or moreelectricity-consuming systems or components onboard the vehicle) withappropriate switching, power conditioning, or power bus(es) for suchon-board electricity-consuming systems or components, for optionaloperation in an alternative fuel cell mode. Inert gas systems withelectrochemical cells that can alternatively operate to produceoxygen-depleted air in a fuel-consuming power production (e.g., fuelcell) mode or a power consumption mode (e.g., electrolyzer cell) aredisclosed in US patent application publication no. 2017/0331131 A1, thedisclosure of which is incorporated herein by reference in its entirety.

With continued reference to FIG. 2 , a cathode supply fluid flow path 22directs gas from a pressurized air source (not shown) into contact withthe cathode 14. Oxygen is electrochemically depleted from air along thecathode fluid flow path 23, and is discharged as oxygen-depleted air(ODA) to an inert gas flow path 24 for delivery to an on-board fuel tank(not shown), or to a vehicle fire suppression system associated with anenclosed space (not shown), or controllably to either or both of avehicle fuel tank or an on-board fire suppression system. An anode fluidflow path 25 is configured to controllably receive an anode supply fluidfrom an anode supply fluid flow path 22′. The anode fluid flow path 25can include water if the electrochemical cell is configured for protontransfer across the separator 12 (e.g., a proton exchange membrane (PEM)electrolyte or phosphoric acid electrolyte). If the electrochemical cellis configured for oxygen anion transfer across the separator 12 (e.g., asolid oxide electrolyte), it can optionally be configured to receive airalong the anode fluid flow path 25. Although not stoichiometricallyrequired by the electrochemical reactions of the solid oxideelectrochemical cell, airflow to the anode during power-consumption modecan have the technical effects of diluting the potentially hazardouspure heated oxygen at the anode, and providing thermal regulation to thecell. If the system is configured for alternative operation in a fuelcell mode, the anode fluid flow path 25 can be configured tocontrollably also receive fuel (e.g., hydrogen for a proton-transfercell, hydrogen or hydrocarbon reformate for a solid oxide cell). Anodeexhaust 26 can, depending on the type of cell and the anode exhaustcontent, be exhausted or subjected to further processing. Control offluid flow along these flow paths can be provided through conduits andvalves (not shown), which can be controlled by a controller 36.

In some embodiments, the chemical inert gas generator 10 can operateutilizing the transfer of protons across the separator 12. Exemplarymaterials from which the electrochemical proton transfer electrolytescan be fabricated include proton-conducting ionomers and ion-exchangeresins. Ion-exchange resins useful as proton conducting materialsinclude hydrocarbon- and fluorocarbon-type resins.

Fluorocarbon-type resins typically exhibit excellent resistance tooxidation by halogen, strong acids, and bases. One family offluorocarbon-type resins having sulfonic acid group functionality isNAFION™ resins (commercially available from E. I. du Pont de Nemours andCompany, Wilmington, Del.). Alternatively, instead of an ion-exchangemembrane, the separator 12 can be comprised of a liquid electrolyte,such as sulfuric or phosphoric acid, which may preferentially beabsorbed in a porous-solid matrix material such as a layer of siliconcarbide or a polymer than can absorb the liquid electrolyte, such aspoly(benzoxazole). These types of alternative “membrane electrolytes”are well known and have been used in other electrochemical cells, suchas phosphoric-acid fuel cells.

During operation of a proton transfer electrochemical cell in theelectrolyzer mode, water at the anode undergoes an electrolysis reactionaccording to the formulaH₂O→½O₂+2H⁺+2e ⁻  (1)The electrons produced by this reaction are drawn from electricalcircuit 18 powered by electric power source 20 connecting the positivelycharged anode 16 with the cathode 14. The hydrogen ions (i.e., protons)produced by this reaction migrate across the separator 12, where theyreact at the cathode 14 with oxygen in the cathode flow path 23 toproduce water according to the formula½O₂+2H⁺+2e ⁻→H₂O  (2)Removal of oxygen from cathode flow path 23 produces oxygen-depleted airexiting the region of the cathode 14. The oxygen evolved at the anode 16by the reaction of formula (1) is discharged as oxygen or anoxygen-enriched air stream as anode exhaust 26.

During operation of a proton transfer electrochemical cell in a fuelcell mode, fuel (e.g., hydrogen) at the anode undergoes anelectrochemical oxidation according to the formulaH₂→2H⁺+2e ⁻  (3)The electrons produced by this reaction flow through electrical circuit18 to provide electric power to an electric power sink (not shown). Thehydrogen ions (i.e., protons) produced by this reaction migrate acrossthe separator 12, where they react at the cathode 14 with oxygen in thecathode flow path 23 to produce water according to the formula (2).½O₂+2H⁺+2e ⁻→H₂O  (2)Removal of oxygen from cathode flow path 23 produces oxygen-depleted airexiting the region of the cathode 14.

As mentioned above, the electrolysis reaction occurring at thepositively charged anode 16 requires water, and the ionic polymers usedfor a PEM electrolyte perform more effectively in the presence of water.Accordingly, in some embodiments, a PEM membrane electrolyte issaturated with water or water vapor. Although the reactions (1) and (2)are stoichiometrically balanced with respect to water so that there isno net consumption of water, in practice moisture will be removed by ODA24 (either entrained or evaporated into the oxygen-depleted air) as itexits from the region of cathode 14. Accordingly, in some exemplaryembodiments, water is circulated past the anode 16 along an anode fluidflow path (and optionally also past the cathode 14). Such watercirculation can also provide cooling for the electrochemical cells. Insome exemplary embodiments, water can be provided at the anode fromhumidity in air along an anode fluid flow path in fluid communicationwith the anode. In other embodiments, the water produced at cathode 14can be captured and recycled to anode 16 (not shown). It should also benoted that, although the embodiments are contemplated where a singleelectrochemical cell is employed, in practice multiple electrochemicalcells will be electrically connected in series with fluid flow to themultiple cathode and anode flow paths routed through manifoldassemblies.

In some embodiments, the chemical inert gas generator 10 can operateutilizing the transfer of oxygen anions across the separator 12.Exemplary materials from which the electrochemical oxygenanion-transporting electrolytes can be fabricated include solid oxidessuch as yttria-stabilized zirconia and/or ceria doped with rare earthmetals. These types of materials are well known and have been used insolid oxide fuel cells (SOFC).

During operation of an oxygen anion transfer electrochemical cell in apower consuming (e.g., electrolyzer) mode, oxygen at the cathodeundergoes an electrochemical reduction reaction according to the formula½O₂+2e ⁻→O⁻  (4)The electrons consumed by this reaction are drawn from electricalcircuit 18 powered by electric power source 20 connecting the positivelycharged anode 16 with the cathode 14. The oxygen anions produced by thisreaction migrate across the separator 12, where they undergo anelectrochemical oxidation reaction at the anode 14 according to theformulaO⁻→½O₂+2e ⁻  (5)Removal of oxygen from cathode flow path 24 produces oxygen-depleted airexiting the region of the cathode 14. The oxygen produced at the anode16 by the reaction of formula (5) is discharged as oxygen or anoxygen-enriched air stream as anode exhaust 26.

During operation of an oxygen ion transfer electrochemical cell in afuel cell mode, oxygen at the cathode undergoes an electrochemicalreduction reaction according to the formula½O₂+2e ⁻→O⁻  (4)The electrons consumed by this reaction are drawn from electronsliberated at the anode, which flow through electrical circuit 18 toprovide electric power to electric power sink (not shown). The oxygenanions produced by this reaction migrate across the separator 12, wherethey react with fuel such as hydrogen at the anode according to theformulaH₂+O⁻→H₂O+2e ⁻  (6)Carbon monoxide (e.g., contained in fuel reformate) can also serve asfuel in solid oxide electrochemical cells. In this case, the oxygenanions produced at the cathode according to formula (4) migrate acrossthe separator 12 where they react with carbon monoxide at the anodeaccording to the formulaCO+O⁻→CO₂+2e ⁻  (7)Removal of oxygen from cathode flow path 24 produces oxygen-depleted airexiting the region of the cathode 14. The steam and carbon dioxideproduced at the anode 16 by the reactions of formulas (6) and (7)respectively is discharged along with unreacted fuel as anode exhaust26. The unreacted fuel that exits anode 16 via anode exhaust flow path26 can be recycled to fuel flow path 32 using an ejector or blower (notshown). It can also be fed to a fuel processing unit wherein the steamand carbon dioxide contribute to reforming.

In an electrochemical system, a plurality of electrochemical cells aretypically arranged in series in a stack via interconnects or bipolarplates as known to those skilled in the art. In FIG. 2 , for simplicitya single anode or cathode can represent the plurality anodes andcathodes of an electrochemical stack. A stack of cells can further bearranged in series, or several stacks of cells can be arranged inparallel according to power availability and requirements.

The ODA produced by each type of chemical inert gas generator needs tobe dried to prevent the formation of ice in the protected space such asfuel tanks. A heat exchanger, water separator, or combination thereofcan be used to condense and remove water from the ODA. In order toefficiently remove sufficient water from the ODA using a heat exchanger,the system must be pressurized to elevate the dew point above freezing.A boost compressor is required to consistently achieve the desiredpressure at the desired point in the system because at some times duringa flight, such as during descent or idle, there is insufficient pressurein the source pressurized air. Exemplary pressurized air sources includebleed air from an engine compressor, a separate compressor which mayprovide pressurized air to the aircraft cabin, or an auxiliarycompressor which provides pressurized air to auxiliary systems.

For example, in some embodiments such as on-board an aircraft duringflight, the condensation temperature at which a desired amount of watercan be removed from the ODA can actually be below 0° C. at ambientpressure, and since it must be operated above 0° C. to avoid icing, aninsufficient amount of water may be removed. However, increasing thepressure of the water-containing ODA can increase the dew point to atemperature above 0° C. for effective removal of water. In anotherexample, in which the system is operated on the ground on a hot day, thetemperature of available outside cooling air on the heat absorption sideof a heat exchanger condenser may not be cold enough to condense adesired amount of water. However, increasing the pressure of thewater-containing ODA can shift the equilibrium toward condensation ofgreater amounts of water, and in some embodiments the pressure at thecondenser can be kept at a level for the dew point to be greater thanambient temperature to provide a maximum amount of water removal. Insome embodiments, pressure can be greater than or equal to 2 atmospheres(atm) absolute pressure. In some embodiments, pressure can be greaterthan or equal to 2 atm absolute pressure, or, greater than or equal to2.5 atm absolute pressure, or, greater than or equal to 2.7 atm absolutepressure. In some embodiments, pressure can be 3 atm absolute pressure.In some embodiments, pressure can be greater than or equal to 3 atmabsolute pressure. In some embodiments, pressure can 2-3 atm absolutepressure.

The boost compressor has a bypass flow path in parallel with thecompressor that has a valve. The valve can be closed to prevent windmilling of the boost compressor rotor when not in use.

The boost compressor is separate from the engine compressor and may beelectrically driven, hydraulically driven, mechanically driven from anaccessory gearbox on the engine, or pneumatically driven using processair from an engine or auxiliary power unit. The boost compressor iscontrolled by a controller. The controller can manage the boostcompressor based on information provided by a sensor or sensors as partof the system or the controller can manage the boost compressor on anoperation schedule. In addition, the controller can manage the ram airflow to the inerting system.

The location of the boost compressor is generally between the source ofpressurized air and the chemical inert gas generator and may bedependent on the method of producing the ODA and the availability ofpower sources. FIG. 3 shows a system and method for producing ODA with areduced water content (also referred to as dry ODA) using a catalyticoxidation inert gas generator. Source pressurized air is optionally sentto a precooler 40 and then sent by a pressurized air flow path to boostcompressor 42 equipped with a bypass valve 44. The boost compressor iscontrolled by the controller 60. If the source pressurized air hassufficient pressure for the system, then the boost compressor isbypassed. If the source pressurized air does not have sufficientpressure, then the boost compressor increases the pressure to thedesired level as described above. The pressurized air is introduced tothe chemical inert gas generator 10. In the embodiment shown in FIG. 3 ,the chemical inert gas generator is a catalytic oxidation unit. Thecatalytic oxidation unit may have an inlet temperature greater than 150degrees Celsius. The chemical inert gas generator discharges humid ODA(via inert gas flow path) which is introduced to a condenser 48 toremove water. Cooling air can be provided to the condenser 48 from ramair or from any suitable heat sink, for example, air conditioned by anair cycle cooling system, or air conditioned by a vapor compressioncycle cooling system, or cabin outflow air. In some embodiments, in lieuof cooling air, a fluid such as chilled liquid ethylene glycol may serveas the heat sink. The cooling source is controlled by controller 60. Thecontroller 60 manages the cooling air temperature to prevent freezingthe condenser 48. The dry ODA exiting the condenser 48 may pass througha sensor 50 and a pressure regulator 52 prior to being introduced to aprotected space such as a fuel tank. Sensor 50 may be used to detecttemperature, pressure, chemical composition or variations thereof and isin communication with controller 60. Pressure regulator 52 may functionin response to controller 60 based, at least in part, on readings fromsensor 50. In an exemplary embodiment, the pressure regulator is set toa constant pressure for the entire mission. In another exemplaryembodiment, the pressure regulator adjusts system pressure according toan operation schedule.

FIG. 4 shows a system in which the chemical inert gas generator 10comprises a proton exchange membrane. Source pressurized air is sent toa precooler 40 and then sent a heat exchanger 54 by a pressurized airflow path prior to boost compressor 42 equipped with a bypass valve 44.The heat exchanger uses ram air as a cold sink and is controlled by thecontroller 60. After the compressor there is a second heat exchanger 62.The second heat exchanger 62 is used to provide air having a temperatureless than the boiling point of water to the electrochemical cell 10. Theboost compressor is also controlled by the controller 60. If the sourcepressurized air has sufficient pressure for the system, then the boostcompressor is bypassed. If the source pressurized air does not havesufficient pressure, then the boost compressor increases the pressure tothe desired level. The pressurized air is introduced to theelectrochemical cell having a proton exchange membrane. Theelectrochemical cell discharges humid ODA which is introduced to acondenser 48 to remove water. Cooling air can be provided to thecondenser 48 from ram air or any suitable heat sink as described above.The cooling air source is controlled by controller 60. The controller 60manages the cooling air temperature to prevent freezing the condenser48. The dry ODA exiting the condenser 48 may pass through a sensor 50and a pressure regulator 52 prior to being introduced to a protectedspace such as a fuel tank. Sensor 50 may be used to detect temperature,mass flow, pressure or a combination thereof and is in communicationwith controller 60. Pressure regulator 52 may function in response tocontroller 60 based, at least in part, on readings from sensor 50 oraccording to an operation schedule.

FIG. 5 shows a system and method for producing dry ODA using anelectrochemical cell comprising a solid oxide electrolyte. Sourcepressurized air is sent to a precooler 40 and then sent by a pressurizedair flow path to boost compressor 42 equipped with a bypass valve 44.The boost compressor is controlled by the controller 60. If the sourcepressurized air has sufficient pressure for the system, then the boostcompressor is bypassed. If the source pressurized air does not havesufficient pressure, then the boost compressor increases the pressure tothe desired level as described above. The pressurized air is optionallypreheated (not shown) prior to being introduced to the chemical inertgas generator 10 comprising a solid oxide unit. Electrochemical cellscomprising solid oxide units may operate at temperatures greater than700 degrees Celsius. The ODA leaving the cathode is sent to a heatexchanger 65 to recover heat which can be recycled to heat the airentering the solid oxide unit if needed. The ODA is then introduced to acondenser 48 to remove water. Cooling air can be provided to thecondenser 48 from ram air or from any suitable heat sink as describedabove. The cooling source is controlled by controller 60. The controller60 manages the cooling air temperature to prevent freezing the condenser48. The dry ODA exiting the condenser 48 may pass through a sensor 50and a pressure regulator 52 prior to being introduced to a protectedspace such as a fuel tank. Sensor 50 may be used to detect temperature,mass flow rate, and pressure and is in communication with controller 60.Pressure regulator 52 may function in response to controller 60 based,at least in part, on readings from sensor 20 or according to anoperation schedule.

In addition to supplying ODA to ullage of the fuel tank(s) onboard theaircraft, the ODA may be also be used for other functions, such asserving as a fire-suppression agent. For example, cargo compartmentsonboard aircraft typically have fire-suppression systems that include adedicated gas-distribution system comprising tubes routed to nozzles inthe cargo bay to deploy fire-suppression agents in the event of a fire.A variety of fire-suppression agents may be deployed depending on thetype and extent of the fire. In the case of a fire, all or some of theODA could be routed to one or more of these fire-suppressiondistribution systems. The ODA could also be used to enable inertingcoverage over extended periods, which may be in addition to, or in lieuof, dedicated low-rate discharge inerting systems in the cargo bay(s).

During operation, the system can be controlled by controller 60 to setfluid flow rates to produce varying amounts of ODA in response to systemparameters. Such system parameters can include, but are not limited tomission phase, temperature of the fuel in protected space(s), oxygencontent of the fuel in the case of a fuel tank protected space, oxygencontent of gas in the protected space(s) 56, and temperature and/orpressure of vapor in the ullage of any fuel tank protected space(s),temperature and pressures in the electrochemical cell 10, andtemperature, oxygen content, and/or humidity level of the inert gas.Accordingly, in some embodiments, the system such as shown in FIGS. 3-5can include sensors for measuring any of the above-mentioned fluid flowrates, temperatures, oxygen levels, humidity levels, or current orvoltage levels, as well as controllable output fans or blowers, orcontrollable fluid flow control valves or gates. These sensors andcontrollable devices can be operatively connected to a systemcontroller. In some embodiments, the system controller can be dedicatedto controlling the fuel tank ullage gas management system, such that itinteracts with other onboard system controllers or with a mastercontroller. In some embodiments, data provided by and control of thefuel tank ullage gas management system can come directly from a mastercontroller.

The term “about”, if used, is intended to include the degree of errorassociated with measurement of the particular quantity based upon theequipment available at the time of filing the application. For example,“about” can include a range of ±8% or 5%, or 2% of a given value.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the presentdisclosure. As used herein, the singular forms “a”, “an” and “the” areintended to include the plural forms as well, unless the context clearlyindicates otherwise. It will be further understood that the terms“comprises” and/or “comprising,” when used in this specification,specify the presence of stated features, integers, steps, operations,elements, and/or components, but do not preclude the presence oraddition of one or more other features, integers, steps, operations,element components, and/or groups thereof.

While the present disclosure has been described with reference to anexemplary embodiment or embodiments, it will be understood by thoseskilled in the art that various changes may be made and equivalents maybe substituted for elements thereof without departing from the scope ofthe present disclosure. In addition, many modifications may be made toadapt a particular situation or material to the teachings of the presentdisclosure without departing from the essential scope thereof.Therefore, it is intended that the present disclosure not be limited tothe particular embodiment disclosed as the best mode contemplated forcarrying out this present disclosure, but that the present disclosurewill include all embodiments falling within the scope of the claims.

What is claimed is:
 1. A system for providing inert gas to a protectedspace, comprising a boost compressor configured to receive pressurizedair and boost a pressure of the pressurized air; a chemical inert gasgenerator; and an inert gas flow path in operative fluid communicationwith the chemical inert gas generator, a condenser and the protectedspace, wherein the condenser operates at a pressure greater than orequal to 2 atmospheres absolute pressure and is located between thechemical inert gas generator and the protected space along the inert gasflow path.
 2. The system of claim 1, wherein the chemical inert gasgenerator comprises a catalytic oxidation unit.
 3. The system of claim2, wherein the catalytic oxidation unit operates at a temperaturegreater than 150° C.
 4. The system of claim 1, wherein the chemicalinert gas generator comprises a proton exchange membrane electrochemicaldevice.
 5. The system of claim 4, wherein the pressurized air flow pathfurther comprises a heat exchanger.
 6. The system of claim 4, whereinthe pressurized air flow path comprises a heat exchanger before theboost compressor and an additional heat exchanger after the boostcompressor.
 7. The system of claim 1, wherein the chemical inert gasgenerator comprises a solid oxide electrochemical device.
 8. The systemof claim 7, wherein the chemical inert gas generator operates at atemperature greater than 700° C.
 9. The system of claim 7, wherein theinert gas flow path further comprises a heat exchanger between thechemical inert gas generator and the compressor.
 10. The system of claim1, wherein the pressurized air flow path comprises a bypass valve inparallel with the boost compressor.